The present application claims priority to Japanese Patent Document No. P2000-301408 filed on Sep. 29, 2000 which is hereby incorporated by reference to the extent permitted by law.
The present invention relates to a fuel cell for producing an electromotive force by reaction of a fuel, such as hydrogen, with oxygen. This invention also relates to a method for the preparation of the fuel cell.
A continuing need exists for an alternative energy source which may take the place of, for example, a fossil fuel, such as petroleum. For example, a hydrogen gas fuel is a desirable alternative and clean energy source. In this regard, hydrogen has a large amount of energy contained per unit weight and, in use, does not emit noxious gases or gases contributing to global warming. Thus, hydrogen is regarded to be an ideal energy source which is clean and, moreover, plentiful in supply.
In particular, fuel cells are generally known to be developed which are capable of recovering electrical energy from energy derived from a hydrogen fuel source. It is generally expected that such fuel cells may be applied in a number of applications, such as, in large scale power generation, on-site self-generation of power or as a power source for an electric vehicle.
The fuel cell typically includes a fuel electrode, such as a hydrogen electrode, and an oxygen electrode, arranged on both sides of a proton conductor film. By supplying fuel (hydrogen) and oxygen to these electrodes, a cell reaction occurs which is utilized to develop an electromotive force. In preparing the fuel cell, the proton conductor film, fuel electrode and the oxygen electrode are routinely molded separately and bonded together.
It is generally accepted that the ability of the fuel cell to facilitate and promote proton conduction during the cell reaction plays an important role in the performance of the fuel cell.
However, typically used proton conductor materials, including a polymer material capable of conducting protons (hydrogen ions), such as perfluorocosulfonic acid resin, generally require to be humidified in order to maintain satisfactory protonic conductivity. In this regard, proton conductivity necessary for a desirable fuel cell performance cannot be maintained in a dry atmosphere using such materials.
Further, the aforementioned polymer material can perform unsatisfactorily with respect to electronic conductivity. This is important because, in the fuel cell, not only protons but also electrons need to be migrated or conducted promptly between and within the terminals. In this regard, the polymer material discussed above is poor in electronic conductivity such that the internal resistance tends to be increased.
It is therefore an advantage of the present invention to provide a fuel cell capable of maintaining optimum proton conductivity even in a dry atmosphere without lowering output of the fuel cell, and a method for the preparation for such a fuel cell.
In an embodiment, the present invention provides a fuel cell having a fuel electrode and an oxygen electrode arranged facing each other with a proton conductor film or film layer disposed therebetween, wherein the fuel electrode and/or the oxygen electrode includes powders of a carbonaceous material as an electrode material such that on the surfaces of said fuel electrode and the oxygen electrode a proton conductor including a carbon-based material mainly composed of carbon and proton dissociative groups introduced in the carbon-based material is provided.
In another embodiment, the present invention provides a method for the preparation of a fuel cell including adding powders of a carbonaceous material as a material for a fuel electrode and/or an oxygen electrode into a solvent containing a proton conductor material including a carbon-based material substantially composed of carbon and a number of proton dissociative groups introduced into the carbon-based material, coating the surfaces of the powder of a carbonaceous material with the proton conductor, and forming at least one of a fuel electrode and an oxygen electrode of the fuel cell.
It should be noted that xe2x80x9cproton dissociative groupsxe2x80x9d means a number of functional groups from which protons (H+) can be detached due to electrical dissociation.
In an embodiment, the proton conductor composed of the carbonaceous or carbon-based material (such as, carbon clusters, e.g., fullerene or carbon nano-tubes) mainly composed of carbon and proton dissociative groups introduced into the carbonaceous material can exhibit optimal and desirably optimum proton conductivity without humidification.
Thus, if such a proton conductor material is additionally present on the surface of the powder of a carbonaceous material as the electrode material, proton conductivity can be sufficiently maintained even in a dry atmosphere.
In addition, since the electrode material coated with the proton conductor is a carbonaceous material, optimum electronic conductivity is provided simultaneously.
According to the present invention, since optimum proton conductivity can be maintained even in a dry atmosphere, optimum proton conductivity may be maintained to provide a fuel cell in which output lowering may be effectively prevented from occurring.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Invention and the Figures.